This research is proposed to investigate the possibility of applying recent new developments in the opticalmonitoring of the number of sickled erythrocytes in a sample of blood. An instrument will be developed to measure this quantity in vitro and non-invasively in vivo. A measurement of this type would offer physicians the opportunity of catching sickle cell crises early in vivo, and the ability to quantitatively evaluate the effectiveness of anti-sickling agents in vitro. The work will be performed in three stages. First the optical scattering coefficient and absorption coefficient will be measured for blood with various hematocrits, with varying hemoglobin oxygen saturations, and possessing varying numbers of sickled cells. Modeling of light flux scattered back from a sample will then be performed using photon diffusion theory and these measured coefficients. Using backscattered light data at two wavelengths, an optical oxymetric technique exists which yields hemoglobin oxygen saturation measurements which are independent of the hematocrit of the mixture. This technique will be applied to the sickle cell blood data, during stage two, in an attempt to obtain an independent measure of the percentage of cells which are sickled. Phase three will test this theoretical development in vitro and in vivo to determine the practicality and accuracy of such a measurement.